Aliens is, in my mind, the best movie, with an actual character arc.
Then Alien, for the style and horror and characters.
Then Resurrection, which while the directing isn't great, it's fun and again has great characters.
Then Alien3, assembly cut.
Then Covenant, which never really differentiated the characters except for main lady, cowboy hat, and religious guy. It had good action, but was weak around that.
Then Prometheus, for dumb people.